In order to ensure earnings in manufacturing of semiconductor wafers, it is important that manufacturing processes thereof are quickly established to promptly shift to a mass production system at a high yield rate.
For this purpose, various inspection/measurement devices have been introduced in a production line. In order to promptly determine process conditions under which desired circuit patterns can be formed, for example, process conditions are intentionally changed to produce plural wafers or chips for inspection at the stage of process establishment, and are determined on the basis of the inspection result. On the other hand, wafers at the stage of mass production are inspected for the purpose of process monitoring. Namely, a wafer sampling inspection is performed during wafer production to check occurrence of defects on the surface of each wafer or to check circuit patterns formed on the surface of each wafer for abnormalities. In the case where defects or abnormalities of circuit patterns are detected as a result of the inspection, the cause is examined to take necessary measures.
As a typical inspection device used at the stage of process establishment or mass production, an optical wafer inspection device is known. For example, Japanese Patent Application Laid-Open Publication No. 2000-97869 (Patent Literature 1) discloses a technique in which an optical image of a wafer surface is captured by bright-field illumination and is compared to an image of a good-quality area (for example, an image of the adjacent chip) to inspect defects. However, such an optical inspection device is affected by the wavelength of illumination, and the resolution limitation of the obtained image becomes about several hundred nanometers. Accordingly, for defects in the order of several dozen nanometers on a wafer, only the presence or absence thereof can be detected. In the case where the defects are analyzed in detail, a defect observer with higher image-capture resolution is additionally necessary.
As a wafer inspection device other than the optical type, a scanning electron microscope (SEM)-type inspection device is known. The device performs an inspection in such a manner that an electron beam is irradiated onto an inspection area on a wafer, and an image obtained by detecting secondary electrons and the like generated therefrom is compared to an image of a good-quality area. Unlike the optical inspection device, image resolution can be increased to the order of nanometer in the SEM-type inspection device. In addition, a defect mode, such as conduction faults of contact holes exposed as electric potential on a wafer surface, that cannot be exposed in an optical image can be inspected. Japanese Patent Application Laid-Open Publication No. 2003-106829 (Patent Literature 2) describes a wafer inspection method by such an SEM-type wafer inspection device.
It is important for a defect inspection device to process in a wide range at high speeds. Thus, the amount of image data is reduced by increasing the pixel size (namely, making the resolution lower) of an image to be obtained as much as possible, and the existence of defects can be confirmed from the detected low-resolution image can be confirmed, but the types of defects cannot be identified in detail in many cases. Accordingly, an observer is used. The observer is a device by which the coordinates of defects of a wafer are captured at high resolution using outputs of an inspection device to output an image. With the advanced miniaturization in a semiconductor manufacturing process, the size of defects accordingly reaches the order of several dozen nanometers. Thus, the resolution in the order of a few nanometers is necessary to observe defects in detail.
Therefore, an observer (hereinafter, referred to as a review SEM) using a scanning electron microscope has been widely used in recent years. Automation of observing work has been desired in a semiconductor mass production line, and the review SEM is provided with an automatic defect review (ADR) function to automatically collect an image at the coordinates of defects in a sample. The coordinates of defects output from the inspection device contain errors, and the defects are detected again from an SEM image captured in a wide viewing field centering on the coordinates of defects output from the inspection device to capture the positions of the defects detected again at high resolution in the ADR.
As a method of detecting defects from the SEM image, Japanese Patent Application Laid-Open Publication No. 2001-189358 (Patent Literature 3) describes a method of detecting defects in which an image obtained by capturing a region where a defect area and the same circuit patterns are formed is used as a non-defective image, and an image obtained by capturing the defect area is compared to the non-defective image. Further, Japanese Patent Application Laid-Open Publication No. 2007-40910 (Patent Literature 4) describes a method of detecting defects from one image obtained by capturing a defect area.
Further, a pattern measurement device is used for a wafer inspection. As an example thereof, a CD-SEM (Critical-Dimension SEM: length measuring SEM) as an SEM-type pattern measurement device is known. The CD-SEM is a device for measuring the line widths of circuit patterns on a wafer at subnanometer measurement accuracy, and is particularly used for management of a semiconductor exposure process. A position to be measured, the template shapes (a line pattern, a hole pattern and the like) of circuit patterns to be measured, measurement items (a line width, a wiring pitch, the diameter of a hole pattern, and the like), and the like are registered in advance in a condition setting file referred to as a recipe. At the time of measurement, an electron beam is irradiated onto each measurement area, and secondary electrons generated therefrom are detected to obtain an image of circuit patterns of an inspection target. Then, a pattern to be measured is searched from the pattern image by pattern matching, and a processing algorithm for computing the set measurement items is applied to the searched pattern for pattern measurement. Japanese Patent Application Laid-Open publication No. 2003-59441 (Patent Literature 5) describes a pattern measurement method in the CD-SEM.